Newbie chuck size question

[Tozguy]

My 12x36 gear head lathe came with an 8’’ four jaw independent chuck. It is more difficult to run this chuck at moderate to high speeds because of vibration. I need a four jaw independent chuck but the 8’’ one seems a bit big for barrel work. A smaller (6’’) four jaw independent direct mounting chuck looks like an interesting option because it might permit higher speeds and would shorten the length through the spindle for barrel work. What do you think? Am I splitting hairs? Thanks for your help. Mike

 

[fastback]

I am sure that a 6-inch chuck will work fine on your lathe. Just keep in mind that the larger the diameter of the work piece the slower you should run the lathe. Your vibration's may be due to speed.

 

[tripletap3]

It may not just be the size. I had the same issue with the 8" 4 jaw "starter" chuck that came with my lathe. At 500-700 rpm it vibrated like a one bladed ceiling fan. After much tweaking thanks to a post from Ray, It improved but I still wasn't happy with it. Actually I think it was more the back plate than the chucks fault. I ended upgrading to a 8" Fuerda Gator direct mount. Best move ever. The vibration is gone and the direct mount cuts the total length and weight way down.

 

[itsme_Bernie]

It probably is too big, as fastback said, but as Tripletap mentioned, it still shouldn't be out of balance.

Mount the chuck, and mount a bar which will fit through the chuck. Indicate the bar to center in the four jaw. Turn the bar down to 60 degrees, like a dead center, at each end. Keep It gripped in the chuck, and remove the chuck from the lathe.

I think you can find a way to crudely mount this setup in a way that you can make it a chuck balancer. Drill some holes in that backplate!


Bernie

 

[ridgeway]

I made a spider mounted to a D1-4 backplate to do barrels on. My chinese 4 jaw does not like speeds above 600 RPM, but who chambers and threads at 600 RPM anyhow? Plus, the spider allows me to do shorter barrels. For what I do, I'd rather have a quality set-tru/zero-tru 3 jaw and chamber in a spider. A smaller diameter 4 jaw will do you fine as long as the through hole is large enough to fit a barrel through.

 

[Tozguy]

Thank you for all your comments..very helpfull!

I had read Ray C's posts on balancing the chuck and back plate. But other recent observations have led me to believe the chuck is defective so balancing will be done once the chuck passes other checks.

Yes it is a 'starter' chuck and doesn't impress so far. I am starting to see a better quality chuck in my future even if it makes me 'cry once'.

Eventually a projet like your spider Ridgeway will be within my capabilities.

Thanks again fellas for your help. Mike

 

[Alphawolf45]

May be too obvious to ask. You have removed the jaws and run the lathe and she then vibrates?

 

[Tozguy]

I went back to confirm that the D1-4 back plate was properly mounted to the spindle and took a cut on the back plate to make sure it runs true.With the chuck remounted on the back plate there is less than .0005’’ TIR on the outside of the chuck body. A test bar that I know is true was indicated it to less than.0005’’ at the chuck. However, 6.5’’ out from the jaws the TIR of the test bar is.015’’. This set up started to shake over 500 rpm. I have run my 6’’ scroll chuck with the same test bar (but with much less runout) to the maximum of 1200 rpm and there was no sign of vibration at any speed.
I had not spun the 8’’ chuck without the jaws. But now that you asked I tried it. Without the jaws it does not vibrate at all up to the maximum of 1200 rpm. At 700 rpm there was only a hint of vibration, but it was nothing like when the jaws are in the chuck. Interesting, thanks Alphawolf.
While the jaws were out I weighed them. One jaw weighs a half once less than the other three.
The jaws seem to be very poorly machined. The holding pads of the jaws do not contact the work evenly. When the outer pad of the jaw contacts the work there is .015’’ of daylight showing under the inner pads.
So now it’s about how to fix the jaws. Unless there is a problem correcting these jaws it does not seem like downsizing to a 6’’ chuck would be worth the expense.

 

[Tozguy]

It looks like the jaws are fixed. The jaws were held concentric to the spindle bore and the inside of the jaws were ground. Now the jaws end up all at the same distance when round work is centered and the scarey vibration it had over 500 RPM is gone. Gonna use this chuck a bit more before replacing it. Thanks for your help folks.

 

[tripletap3]

It looks like the jaws are fixed. The jaws were held concentric to the spindle bore and the inside of the jaws were ground. Now the jaws end up all at the same distance when round work is centered and the scarey vibration it had over 500 RPM is gone. Gonna use this chuck a bit more before replacing it. Thanks for your help folks.

The jaws were another reason why I replaced the chuck I had. The new Gator has much nicer 2 piece jaws.